1. Field of the Invention
This invention relates to shrinkable sleeves suitable for use in covering joints and terminations in electrical cables adapted to carry voltages of 1 KV or more.
2. Summary of the Prior Art
It is known to use shrinkable sleeves to cover joints and terminations in electrical cables adapted to carry voltages of 1 KV or more. Such sleeves generally comprise an insulating layer and either or both of (a) a conductive layer outside the insulating layer, and (b) a layer inside the insulating layer which is conductive or semi-conductive or provides electrical stress control. Reference may be made for example to U.S. Pat. Nos. 3,717,717, 3,950,604 and 4,001,128. In such sleeves, each of the layers may be independently heat-shrinkable, as for example in the sleeves described in U.S. Pat. No. 3,717,717. However, as disclosed in U.S. Pat. Nos. 4,035,534, 4,070,746 and 4,135,553 and in copending commonly assigned Application Ser. No. 586,901 by Joseph Krackeler et al., it is also possible to make shrinkable multi-layer sleeves in which at least one of the layers is a tube of elastomeric material which is maintained in the stretched condition by another layer, the other layer being heat-shrinkable, or heat-softenable, or removable. The disclosures of the U.S. Patents and application referred to above are incorporated herein by reference.
In many of the shrinkable sleeves of the prior art, the insulating layer, which is relatively thick compared to the other layer or layers, has a constant internal diameter and an outer diameter which gradually decreases at each end of the sleeve. This provides a desirable profile for the shrunken sleeve and, when there is a conductive layer outside the insulating layer, brings the conductive layer into contact with, or close proximity to, the cable shield. In sleeves which include a conductive, semi-conductive or stress control layer inside the insulating layer, many designs show this layer recessed into the central section of the insulating layer. In order to make sleeves in which the insulating sleeve is shaped, for example as described above, it has heretofore been necessary to use molding techniques which are slow and expensive.